You'll be amazed at what a difference a little flash light can make, and knowing how to use a flash can have a lot of value if you get into a low light situation. Flashes are useful indoors in ballrooms, churches, wedding receptions and corporate events. Flashes can be useful outdoors as fill in light or on a sunny day to overpower the sun and avoid intense shadows and hot spots. Both the 480EX III-RT and the 600 EX-RT can be used on camera and as 'slave' units. The ST-E3-RT transmitter is compatible with the 430EX III-RT and the 600 EX-RT, and can control up to 5 groups, or 15 individual flashes. The MT-24EX flash is specifically designed for macro photography.